Investigation of hot carrier effects on RF CMOS integrated circuits.

摘要

With the continual down-scaling of the channel length of MOSFETs, CMOS technology is being increasingly used for the implementation of radio frequency (RF) circuits and systems. However, with technological scale down of dimensions, the supply voltage is not reduced in the same proportion as the channel length, leading to the presence of strong electric fields in the device. Carriers which go through these strong fields gain high energy and are called "hot carriers." Hot carriers (HC) damage the gate oxide by generating interface traps and trapped charges in the oxide which lead to degradation of the device's performance.; In this thesis, the effects of HC on the DC and RF performance of submicron NMOSFETs were studied. The main HC effects on the DC performance are an increase of the threshold voltage and a decrease of channel carrier mobility. In the small-signal model, these effects appear as a decrease of the transconductance gm and increase of output conductance gds . The degradation of the device's RF performance such as unity-current gain frequency or maximum oscillation frequency is essentially due to the degradation of device's DC performance.; To explore the HC effects on RF circuits, negative resistance oscillators made with CMOS and subjected to HC stress were investigated. The mechanism of operation of these oscillators was studied and, unlike previous analyses, a clear explanation of how the oscillation amplitude reaches to a stable value is presented. Research shows that as long as biasing current of the oscillator circuit is not affected by hot carries, then the operation of oscillator is unaffected. However, if biasing current changes due to stress, then the oscillation amplitude may change, affecting other performance characteristics of the oscillator.; For the low noise amplifier (LNA) studied, the important effect of hot carriers is a drop of its gain. As a result of the decrease in gain, the noise figure of the LNA increased. It was found that linearity properties of the LNA depend on the operating point of the device and can improve after stress.